Hearing devices are portable hearing apparatuses that are used to assist the hard-of-hearing. To accommodate the numerous individual needs, different types of hearing aids are provided, such as behind-the-ear (BTE) hearing aids, hearing aids with an external earpiece (RIC: receiver in the canal) and in-the-ear (ITE) hearing aids e.g. also concha hearing aids or completely in the canal (CIC) hearing aids. The hearing devices cited by way of example are worn on the outer ear or in the ear canal. In addition, however, there are also bone conduction hearing aids, and implantable or vibrotactile hearing aids available on the market. In these housings the damaged hearing is stimulated either mechanically or electrically.
The main components of hearing aids are essentially an input transducer, an amplifier and an output transducer. The input transducer is normally an acoustic receiver e.g. a microphone, and/or an electromagnetic receiver e.g. an induction coil. The output transducer is usually implemented as an electro-acoustic transducer e.g. a miniature loudspeaker, or as an electromechanical transducer e.g. a bone conduction earpiece. The amplifier is usually integrated in a signal processing unit. This theoretical design is shown in FIG. 1 using the example of a behind-the-ear hearing aid. One or more microphones 2 for picking up the ambient sound are built into a hearing device housing 1 for wearing behind the ear. A signal processing unit 3, which is also built into the hearing aid housing 1, processes and amplifies the microphone signals. The output signal from the signal processing unit 3 is transmitted to a loudspeaker or earpiece 4, which outputs an acoustic signal. If necessary, the sound is transferred to the eardrum of the hearing device wearer via a sound tube that is fixed to an ear mold in the ear canal. A battery 5, which is also built into the hearing device housing 1, supplies power to the hearing device and in particular to the signal processing unit 3.
Acoustic signals that are picked up by one or more microphones of a hearing device are usually decomposed into sub-band signals for further processing. This is normally done using one or more frequency-selective digital analysis filter banks (AFB), by means of which K>1 sub-band signals are obtained. Sub-band-specific signal manipulations can be performed after the decomposition. The manipulated sub-band signals can subsequently be re-synthesized using a digital synthesis filter bank (SFB).